Was asked about secondary dominants recently. Also about secondary extended dominants.
From a bit of research, it seems there are two views on what the latter are. Could be extended (dominant) chords - as in 9ths, 11ths, 13ths, with/out alterations. Usually in root position, with notes expanding past the octave. Or - dominant chords which move to another dominant , as in key C, the A7 that moves to D7.
I can understand extended chords as such, and also extended chord sequences, which the second definition nods towards. but the two definitions just don't appear to align.
I guess in the latter, key C, A7 going to Dm7 wouldn't qualify as an extended secondary (secondary extended?) chord. Any thoughts?